This proposal requests continued support of an ongoing research effort regarding vestibulo-ocular function in the elderly. The proposed experiments address several specific hypotheses concerning the influence of age on the vestibular system and its interaction with other sensory systems and cognitive processing. The proposed research builds upon work performed in the previous two grant cycles and will examine the influence of aging on 1) interference between attentional processes and vestibular-induced eye movements, 2) interference between attentional processes and visually-induced eye movements, and 3) visual-vestibular interaction. Interference is conceptualized as occurring at one or more stages of two sensory-motor processes. Dual-task paradigms will be used to address specific hypotheses about the interference between attention and visuo-vestibulo-ocular motor function. Responses of healthy older individuals will be compared with those of younger subjects. We will extend our studies to persons who are older than those previously tested by evaluating two groups of older subjects, one aged 65-74 years and the other aged 75-84 years, since age-related impairments of balance often begin in the early to middle seventies. Vestibular stimulation will activate both the semicircular canals and otolith organs. Visual stimuli will include stationary and both predictable and unpredictable target motion. Eye movements will be measured with video-oculography and the magnetic sclera search coil technique. Cognitive tasks will include both choice reaction time and disjunctive reaction time tasks using auditory cues that differ in either pitch or side of presentation. As correlative measures, all subjects will undergo dual-task paradigms of upright balance while performing a concurrent reaction time task. The neuropsychological status of the older subjects will be assessed using a validated battery of cognitive function tests to rule out dementia and a specialized test battery to assess three subtypes of attentional abilities. Taken together, these studies will provide essential information regarding the influence of aging on several specific aspects of balance and thus may have practical implications regarding the management of age-related loss of balance.